Environmental testing — thermal vacuum (TVAC), vibration, acoustic, EMC - EMI: Foundations

3.6.33 · D1 · Physics › Spacecraft Structures & Systems Engineering › Environmental testing — thermal vacuum (TVAC), vibration, ac

Is page par assume kiya gaya hai ki aap kuch nahi jaante. Parent note ka har letter — $σ$ , $ε$ , $T^{4}$ , $ω_{n}$ , $ζ$ , $Q$ , $Tr$ , $g_{r m s}$ , PSD, dB, Torr — yahan ground up se build hoga. Agar koi symbol parent mein aata hai, to woh neeche pehle define hoga, uske baad aapse use trust karne ko kaha jayega.

Part A — Numbers jo "kitna hot hai" describe karte hain

Temperature $T$ aur Kelvin scale

Picture yeh socho: ek bag mein chhote bouncing balls hain. Thanda = balls muskil se hilte hain; garam = balls wildly slam karte hain. Kelvin "bilkul koi motion nahi" se count karta hai.

Celsius se convert karne ke liye: $T_{K} = T_{^{\circ} C} + 273.15$

Toh room temperature $20^{\circ} C = 293 K$ , aur space ka background lagbhag $3$ K hai — almost totally still.

Figure s01 mein do thermometers side by side hain — Celsius left par, Kelvin right par — absolute zero, pani ke freezing point, room temperature, aur TVAC hot soak ke colored dots ke saath. Koi bhi horizontal arrow follow karo: physical point identical hai, bas scale par number $273.15$ se shift hota hai. Dekho absolute zero Celsius rod par $- 273.15$ par baith ta hai par Kelvin rod par $0$ par — yahi poori wajah hai ki hum Kelvin prefer karte hain.

Figure — Environmental testing — thermal vacuum (TVAC), vibration, acoustic, EMC - EMI

Part B — Heat kaise travel karta hai (aur vacuum yeh kyun change karta hai)

Heat travel karne ke exactly teen tarike hain. Space kyun special hai yeh dekhne ke liye aapko teeno jaanne chahiye — aur, jaise promise kiya, har ek ko sirf ek word nahi, ek symbol aur ek law milega.

Figure s02 mein ek red hot block hai jiske teeno exits hain: left mein solid bar ke saath conduction dikhata ek blue arrow, upar uthti warm air ke green arrows (convection) — labelled "GONE in vacuum" — aur right mein ek yellow wavy infrared arrow (radiation) jo bina air ke bhi survive karta hai.

Formula Har path ka law (woh symbols jo aage milenge)

Conduction — Fourier's law. Ek solid ke through heat flow yeh hai: $Q_{cond} = - k_{th} A \frac{Δ T}{L}$ jahan $k_{th}$ = thermal conductivity (W/(m·K), material kitni aasani se heat pass karta hai), $A$ = cross-section area, $Δ T$ = uske across temperature difference, $L$ = uski length. Bada $k_{th}$ ya bada $Δ T$ = zyada heat crawl karti hai.
Convection — Newton's law of cooling. $Q_{conv} = h A (T_{s} - T_{\infty})$ jahan $h$ = convective coefficient (W/(m²·K), fluid kitne vigour se heat carry away karta hai), $T_{s}$ = surface temperature, $T_{\infty}$ = surrounding fluid temperature. Vacuum mein $h \to 0$ , isliye yeh poora term vanish ho jaata hai — quantitative reason ki convection kyun disappear ho jaati hai.
Radiation — Stefan–Boltzmann law (Part C mein build hoga).

Part C — Radiation formula symbol by symbol build karna

Parent ki headline formula $q = σ ε T^{4}$ hai. Har piece earn karte hain.

Area $A$

$A$ simply kitni surface radiation kar rahi hai, square metres ( $m^{2}$ ) mein. Badi radiating surface → zyada heat escape, exactly jaise bada window zyada light nikalne deta hai.

Emissivity $ε$ (Greek letter "epsilon")

Do identical hot plates socho: ek matte-black wala strong infrared throw kar raha hai, ek shiny wala muskil se glow kar raha hai. Same temperature, bahut alag $ε$ .

Absorptivity $α$ (Greek "alpha")

$ε$ ka twin: $α$ woh fraction hai jo incoming light ek surface soak up karti hai (baaki bounce off hoti hai). Solar panel par sunlight $α$ se govern hoti hai; usse nikalne wali heat $ε$ se govern hoti hai.

Stefan–Boltzmann constant $σ$ (Greek "sigma")

Fourth power, $T^{4}$ kyun?

Figure s03 mein $q = σ ε T^{4}$ temperature ke against plot hai. $300$ K aur $350$ K par do blue dashed markers height jump seedha curve se read karne dete hain — green label $\approx 1.85 \times$ increase dikhata hai sirf $50$ K rise ke liye. Steepness hai fourth power visible ho raha hai.

Ab poora formula plain words mein padhta hai:

Part D — Pressure aur "vacuum" ka matlab

Ek kamra socho logon se bhara hua (760 Torr) jo dheere dheere khaali ho jaata hai jab tak ek hi insaan ek city block mein wanders kare ( $1 0^{- 5}$ Torr).

Part E — Shaking: vibration symbols

Mass $m$ , stiffness $k$ , damping $c$

Figure s04 (left panel) schematic hai: ek yellow mass $m$ blue spring $k$ aur green damper $c$ se ceiling se hang kar raha hai, red double-arrow uski displacement $x (t)$ mark karta hai. Right panel payoff hai — ek plot jo aapko aage study karna chahiye.

$\overset{x}{¨}$ aur $\overset{x}{˙}$ mein dots ka matlab hai time ke saath change ki rates: $\overset{x}{˙}$ = velocity (kitni tezi se move karta hai), $\overset{x}{¨}$ = acceleration (velocity kitni tezi se change hoti hai). Hamein yeh chahiye kyunki Newton's law force ko acceleration se connect karta hai.

Natural frequency $ω_{n}$ aur $f_{n}$

Damping ratio $ζ$ aur quality factor $Q$

Resonance aur transmissibility $Tr$

PSD, g²/Hz, aur $g_{r m s}$

Decibels (dB) sound aur slopes ke liye

Part F — Electromagnetic noise (EMC/EMI symbols)

Yeh foundations topic mein kaise feed karte hain

Yeh seedhe parent topic mein feed karte hain, aur bahar connect karte hain Spacecraft Thermal Control Systems, Launch Vehicle Dynamics, Structural Mechanics, Electromagnetic Wave Propagation, Reliability Engineering, aur Quality Assurance in Aerospace se.

Equipment checklist

Khud test karo — kya aap bina dekhey har ek state kar sakte ho?

T

kya measure karta hai aur radiation laws mein kaun si unit use karni chahiye?

Atoms ki absolute jiggling; Kelvin mein honi chahiye (zero = absolute zero).

Vacuum mein teen heat paths mein se kaun si disappear hoti hai, aur kis coefficient ke zariye?

Convection — iska coefficient

h \to 0

ho jaata hai (Newton's law of cooling

Q_{conv} = h A (T_{s} - T_{\infty})

Fourier's law of conduction state karo aur har symbol name karo.

Q_{cond} = - k_{th} A Δ T / L

; thermal conductivity, area, temperature difference, length.

Emissivity

ε = 0

ε = 1

ka kya matlab hai?

0 = perfect mirror (koi glow nahi); 1 = perfect blackbody (max glow).

Radiated power

\propto T^{4}

kyun hai,

T

kyun nahi?

Hotter surfaces har colour par zyada emit karti hain aur higher-energy colours ki taraf shift hoti hain; combined se fourth-power law milta hai.

NET radiative exchange likho (sirf emission nahi).

Q_{rad} = A σ ε (T_{s}^{4} - T_{amb}^{4})

, view factors se weighted.

Normal sea-level air Torr mein kitna hai, aur hard vacuum kitna hai?

~760 Torr sea level par; ~

1 0^{- 5}

Torr hard vacuum hai.

Natural frequency formula likho aur batao

k

badhane se kya hota hai.

ω_{n} = k / m

; stiffer

k

frequency raise karta hai (tezi se wobble).

ω_{n}

f_{n}

Hz mein convert karo.

f_{n} = ω_{n} / (2 π)

ζ

ke terms mein

Q

kya hai, aur

ζ = 0.02

kya deta hai?

Q = 1/ (2 ζ)

;

ζ = 0.02 \Rightarrow Q = 25

Resonance par (

r = 1

) transmissibility

Tr

kya hai?

Tr = Q

(maximum amplification).

g_{r m s}

mein

f_{1}

f_{2}

aur

G (f)

kya hain?

Band ki low/high frequencies (jaise 20 aur 2000 Hz) aur PSD function g²/Hz mein.

Sound pressure dB mein,

0

dB kya hai aur

10 lo g

20 lo g

use karte hain?

0

dB = reference

20 μ

Pa; amplitude (pressure) ratios ke liye

20 lo g_{10}

use karo.

EMI aur EMC mein kya difference hai?

EMI = unwanted interference; EMC = subsystems ka bina interfere kiye coexist karne ka goal.

Recall Quick self-quiz

Stefan–Boltzmann law mein $T$ ki kaun si power aati hai? ::: Chauthi power, $T^{4}$ . Celsius mein absolute zero? ::: $- 273.15^{\circ} C$ . $Q = 25$ ke saath resonance par $1 g$ input kya ban jaata hai? ::: $25 g$ . $Q_{rad}$ subscripted kyun hai par $Q$ nahi? ::: $Q_{rad}$ = radiated heat (watts); $Q$ = vibration quality factor — do unrelated quantities.